Embodiments described herein relate to the use of three-way catalysts in reducing carbon monoxide, nitrogen oxides (NOx), and hydrocarbon emissions from vehicle exhausts, and more particularly, to a three-way catalyst comprising a mixture of nickel and copper.
In recent years, government regulations in the United States have restricted emissions of carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) from vehicle engine exhausts. This has necessitated the use of catalysts in gasoline and diesel powered vehicles which function to stimulate the oxidation reaction of HC and CO and the reduction of NOx. Such catalysts are typically referred to as three-way conversion (TWC) catalysts because they simultaneously oxidize CO and HC to CO2 and water while reducing NOx to nitrogen. Three-way conversion catalysts often include materials with oxygen storage capacity (OSC), i.e., materials which provide additional oxygen needed to oxidize carbon monoxide and hydrocarbons in the exhaust at rich air/fuel ratios. During subsequent lean air/fuel operations, the excess oxygen in the exhaust then replenishes the depleted oxygen of the OSC materials used in the previous rich operations, which enhances the overall reduction of NOx in the exhaust stream. Such OSC materials typically comprise cerium-based oxides such as cerium oxide (CeO2), cerium-zirconium mixed oxides (CexZryO2), and cerium-praseodymium mixed oxides (CexPryO2).
However, in some vehicle operations with long and rich air/fuel excursions, conventional cerium-based oxides do not generate sufficient amounts of oxygen needed for the oxidation of HC and CO. In commonly-assigned application Ser. No. 13/367,692, a nickel-based catalyst is described which provides additional OSC function as well as water-gas-shift activity to a conventional three-way catalyst aftertreatment system.
However, it would be desirable to provide enhanced OSC and WGS functions to improve the reduction of emissions of carbon monoxide, hydrocarbons, and nitrogen oxides.
Accordingly, there is a need in the art for a three-way catalyst which provides reduction of carbon monoxide, nitrogen oxides, and hydrocarbon emissions from vehicle exhausts, and to a catalyst having enhanced oxygen storage capacity and enhanced reduction of carbon monoxide or hydrocarbons via a catalyst water-gas-shift reaction.